Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.41   7.283%   $223.5885   $223.59   $223.60   $223.60  
  Purchase #2 $179.40   8.271%   $194.2382   $194.24   $194.25   $194.20  
  Purchase #3 $168.59   4.119%   $175.5342   $175.53   $175.55   $175.50  
  Purchase #4 $156.33   6.753%   $166.887   $166.89   $166.90   $166.90  
  Purchase #5 $243.95   5.487%   $257.3355   $257.34   $257.35   $257.30  
  Purchase #6 $114.77   12.360%   $128.9556   $128.96   $128.95   $129.00  
  Purchase #7 $236.94   12.828%   $267.3347   $267.33   $267.35   $267.30  
  7 purchase totals = $1,308.39       $1,413.8737   $1,413.88   $1,413.95   $1,413.80